Add adapter session codecs with cwd-aware resume and unknown-session retry

Introduce AdapterSessionCodec interface for structured session serialization,
deserialization, and display ID extraction. Implement codecs for claude_local
and codex_local adapters with cwd validation — sessions saved for a different
working directory are not resumed. Both adapters now return sessionParams and
sessionDisplayId alongside legacy sessionId.

Add isCodexUnknownSessionError detection and automatic retry with fresh session
for codex_local (matching existing claude_local behavior). Inject approval
context env vars (PAPERCLIP_APPROVAL_ID, PAPERCLIP_APPROVAL_STATUS,
PAPERCLIP_LINKED_ISSUE_IDS) into adapter environments.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/__tests__/adapter-session-codecs.test.ts

@@ -0,0 +1,64 @@
+import { describe, expect, it } from "vitest";
+import { sessionCodec as claudeSessionCodec } from "@paperclip/adapter-claude-local/server";
+import { sessionCodec as codexSessionCodec, isCodexUnknownSessionError } from "@paperclip/adapter-codex-local/server";
+
+describe("adapter session codecs", () => {
+  it("normalizes claude session params with cwd", () => {
+    const parsed = claudeSessionCodec.deserialize({
+      session_id: "claude-session-1",
+      folder: "/tmp/workspace",
+    });
+    expect(parsed).toEqual({
+      sessionId: "claude-session-1",
+      cwd: "/tmp/workspace",
+    });
+
+    const serialized = claudeSessionCodec.serialize(parsed);
+    expect(serialized).toEqual({
+      sessionId: "claude-session-1",
+      cwd: "/tmp/workspace",
+    });
+    expect(claudeSessionCodec.getDisplayId?.(serialized ?? null)).toBe("claude-session-1");
+  });
+
+  it("normalizes codex session params with cwd", () => {
+    const parsed = codexSessionCodec.deserialize({
+      sessionId: "codex-session-1",
+      cwd: "/tmp/codex",
+    });
+    expect(parsed).toEqual({
+      sessionId: "codex-session-1",
+      cwd: "/tmp/codex",
+    });
+
+    const serialized = codexSessionCodec.serialize(parsed);
+    expect(serialized).toEqual({
+      sessionId: "codex-session-1",
+      cwd: "/tmp/codex",
+    });
+    expect(codexSessionCodec.getDisplayId?.(serialized ?? null)).toBe("codex-session-1");
+  });
+});
+
+describe("codex resume recovery detection", () => {
+  it("detects unknown session errors from codex output", () => {
+    expect(
+      isCodexUnknownSessionError(
+        '{"type":"error","message":"Unknown session id abc"}',
+        "",
+      ),
+    ).toBe(true);
+    expect(
+      isCodexUnknownSessionError(
+        "",
+        "thread 123 not found",
+      ),
+    ).toBe(true);
+    expect(
+      isCodexUnknownSessionError(
+        '{"type":"result","ok":true}',
+        "",
+      ),
+    ).toBe(false);
+  });
+});